Compression tester for plastic materials



` April 28, `1942;` A A. NADA! ETAL 2,280,966

\ `coMPREssToN TEsTEE EOE PLASTIC MATERIALS Filed Jan. 26, 1940 WITNESSES:`

A EY Patented Apr. `28,` 1942 commission TESTER Foa rLAsTrc ArpadNadai and Harold C. Harrison, Wilkinsburg, Pa., assignors to Westinghouse.mectric M Manufactum!! Company, `East Pittsburgh, c I Pa., a corporation of Pennsylvania v v M f 1 Application `.mamy ze, 1940, serial No. 315,698

` (crass-12) A in claims.

. Our invention relates to testlngthe mechanical properties of plastic materiaLand it has particular relation to a machine forttesting the plastlcity of `wet clay or porcelain earth such as are used for making porcelain `insulators v and. other ceramic bodies.

A mA reliable meansrof testing thepiasticity of Iwet clay `has long been needed `in; the ceramic industry. Recently a torsion machine was sug- `gested for this `purpose but since `the tensile strength of wet clay orporcelain earthl is very small, the specimens soonl break in tension and` thuslfail to give an adequate indication of their mechanical properties.` I

Since clay and :porcelain earth are actually deformed under compression in commercial practice, the lideal test for these substances is the i. compression test ofta cylindrical specimen. `A`

serious disadvantagahoweven is caused by the lateral `spreading of the test cylinder of clay when it is deformedby compression in such a test. Also the rate at which the cylinder is com- I `which `is secured to a base 2 `carries spaced supporting plates I and l between which pass aV pair of stationary verticalbars and 6. A split I cross-piece 1, carrying a pair ofeyebolts B, is

secured to the support I in a vertically adjustable position by bolts 9 which when tightened cause the two portionsof thecross-piece to frictionally engage the bars 5 and 6.` l Supporting plate 3, cross-piece 1 and supporting plate l are provided with aligned `circular holes 'throughl which ex- I `tends a supporting rod liicarryingat its lower pressed shouldbe clearly; deiined and kept constant, which requirement would ordinarily make it; necessary 1to provide `very complicated speed controls. I

By `means of `our invention, the above disadvantages ofthe ordinary; compression test are overcome. In the iirst place, the `test cylinder is compressed at such `velocity of the compression plates that the compressionratestays essentially constant. Rotating cutting wires keep the `diameter of the clay` cylinder constant so that theload isan indication `of the stress, and dimculties `resulting from thelateral spreading `of the clay` are entirely eliminated., y I

Ict isaccordingly, `an object` of our invention lto `provide apparatus `for testing the` mechanical properties of I plastic material.` 1

i `More speciilcally stated, itis an `object of our invention to provide improved apparatus for appLving a compression test to` wet .clayandporce- I lain earth todetermine themechanical proper- `ties thereof; I o I I Othercobjects of lour invention willbecome evident :from` the following detailed `description `.taken in` conjunction ;with the accompanying drawing, in -which like parts are designatedyby like reference characters throughout the various ""Inthedrawingg 1 y y u I `Figure `1 is a view in perspective oi testing apparatus `built inaccordance` with my invention,

Fig.`2 is an enlarged cross-sectional view taken along the line II--III of Fig. 1,`

s 1 3 is a diagrammatic viewof the `indicating mechanism employed on the apparatusotFig. 1, Fig. `i is a graph illustrating the construction ofthe cam shown on theapparatus in Fig; 1.

I c Referringto Figli of the;drawing,la standard `end the upper plate Il of a pair of `circular coinpression plates` II and I2.\

`disposed on supportingIplates 3 and 4, respec- Rollers`i3 and I4 tively, actas guides for the rods `lll inits vertical movement. Adjustably securedto this rod I0 at t a point between the lower supporting plate I and the cross--piece` 1` in any suitable manner is a split I metalclamp I5 having `two pairs of relatively small holes near its `upper `anci lower edges for receiving the ends of two pairs of helical springs` II` and I1. The upper ends of springs I6 are eachsecured` to one of the `eyebolts` Il on the cross-piece 1,1 and the lowerendsof springs I1 areeach attached to one of a pairof eyebolts I8 carried by the lower supporting plate 4. Accordinglyftherodvi is resiliently` supported in position. An arrangement including a pulley I9 and rope 20 isprovided to `counterweight this rod I0. y The lowerucompresson` plate` I2 is secured to y the upper endof a supporting rod 2l which passes freelythrough` a guide or `bearing 22 and carries a roller 23 at its lower end.` The rroller 23 rests upon the curved-surface of a cam 24, the lower `edge of which` is seated in a horizontal guide 25.

An `internally screw-threaded member 26` is fixed to the forward part of the cam and engages` a screw-threaded shaft 21 of c a pulley 2li.` A belt connects the pulley 28 with a second pulley 29 driven by a motor I0: and by using other pulleys of different diameters `a desired speed` ratio between the shaft 21 and motor l0 may be obtained. The cam `24 is preferably designed with such a curved surface `that when it iswmoved horizontally toward thelpulley 28 at a constant velocity,.

a test cylinder A of plastic material disposed between; the plates `II and I I2 is compressed at a constantrate of1strairi.` i A more detailed discussion of the; shape of this cam will be found hereinafter.1v j A circular plate member 3|` of largerdiameter than the compression `plates II and I2 has an integral concentric bearing portion 32 with' an `interior bearing surface contacting the surface `of the supporting rod III and is rotatable thereabout,` A similar vplate member 23 is provided with a `downwardly extending integral bearing portion I4 having its interior or bearing surface in rotatable engagement with the supporting rod 2l. `.Il pair of diametrically opposed vertical rods test piece.

35 aresecured to the plates 3| and 33 to maintain them in spaced relationship,l as indicated, and two pairs of vertically spaced horizontal arms 35, each pair carrying a pair of wines 31 and 38 are adjustably secured to the rods 35.

Secured to the outside of the lower bearing portion 34 is a pulley 39 arranged to be drivenV by a belt 40 which is in turn driven by the motor 30. The pulley 39 is rotatably supported on an annular bearing portion formed on the upper surface of a disk 4|, the purpose of which will be hereinafter described. It will be evident that the rotation of the pulley 39 will result in the wires 31 and 38 rotating about the axis of the test piece A.

. f The rotating cutter mechanism will be better understood upon reference to the horizontal sectional 4view of Fig..2 whereinY the same parts are designated by the `same reference characters as inFig. 1`. Both pairs of Wires 31, 38 are disposed substantially parallel to the axis ofthe test cylinder and, for rotation of the plate` 33 in the dis rection indicated by the arrow, the leading wire 31 of each pair is arranged to either contact or verynearly contact the peripheries of the compression plates and I2. The function of vthe wire 31 is'to out away that part of the test cylinder A which bulges out at the sides during the test. These wires must be relatively thin in order to make a clean cut, and, Vbecause of their ysmall cross-section, often permit the cut fragments to adhere to the surface of the test piece. In order to prevent these scraps from disturbing the results of the test We prefer to provide 'the second wire 38, trailing the cutting wire 31 and .A displaced slightly from the surface of the test cylinder. While it has been found that in xnost -cases one such additional wiresatisfactorily removes these scraps,` it will be evident that the number of wires may be changed as desired.

g The disk 4| forms the bottom of a guard 42 for collecting the ,fragments from the test Vcylinder and thus preventing them from scattering on the apparatus and surroundings. The remainder of this guard preferably comprises a cylindrical portion made up of .atpair ,of conveniently connectable sections, only one of which is shown.

The stress-strain v'curve of the test cylinder VA is automatically indicated on a glass plate'43 covered with lamp black or paper. An arm 44, having at one end a stylus 45 and pivoted at its other end about a pin 461on the supporting rod I0, is pivotally secured at a point intermediate its ends to the standard by a pin 41. The vertical movement of therod I and consequently that of the stylus The recording plate 43-is arranged for horlzontal `movement within'a` supporting frame 48 and, as is betterv shown in Fig. 3,` has a light belt Vor cord 48 attached to its inner end. 'I'his cord 49 passes horizontally over va stationary pulley 50`whlch may be attached to the standard I andifrom there extends vertically downward to another pulley I which is secured to the movable lower supportingrod .2|. After passing over the pulley 5| the cord extends vertically upward and is ,attached at its end to a stud 52 disposed on the 'upper supporting rod I0. Attached to the'outslde end of the plate 43 is another cord 5,3 which passes horizontally to `a pulley 54 disposed on the supporting frame 49 and carries a weight 55 on its other end. The purpose of the weight 55 is'to retain the cord 49 taut so that the horizontal movement of the 45 indicates the stress on the Y where distance between pulley 5| and the stud 52 and consequently to the change in height of the test piece A during a test.

The cam 24 for compressing the test piece may be of the same shape as the cross-hatched area which is partly bounded by the curve C of Fig. 4. This curve is an exponential having the equation h=h0e7l in'which h represents the height and is plotted vertically `while t represents the time and is plotted horizontally. The constant 1z0-represents the height of the test piece A at the start of the compression test. As is desirable, in order to obtain uniform results insuch a test, the true strain rate v, which is negative inv thecase of a compression test, is maintainedV constant.

-That a uniform strain rate results when the cam 24 is designed inaccordance with the above can be demonstrated as follows: Y

The true compression rate 5 of the test piece A is given by the following equationz' K i i l Iv l Y u h=h0e" where v 1snegat1ve for a compression test The operation of the above described apparatus may be set forth as followszThe cam 24 is located at its position most remote from the screw `threaded shaft 21 and the substantially cylindrical test piece A, extruded from the batch of wet clay or porcelain earth, is disposed between the plates and |2 which are then` at the posi tions most remote from each other. The glass plate 43 with'its covering of lamp black is positioned at the left end of its travel as shown on the drawing. 'Ihe motor 30 is operated to drive thepulley--ZB at a selected constant speed, thus moving the cam 24 horizontally at a constant velocity and compressing the test cylinderA at a uniform rate. At the same time the pulley 39 is driven rotating theY cutting mechanism including the wires 31 and 38 to maintain the cross-section of the test piece constant. At the same time, the stress-strain curve is recorded on the glass plate. The guard 42 prevents the fragments of clay cut off by these wires from falling onto the apparatus or surroundings. out the `test the vertical position of the stylus 45 will indicate the stressv on the 'test cylinder A while the indicating plate 43 will move horizontally in -accordance with the resulting strain.

Although we haveshown and described a specific embodiment of our invention, we 'are fully aware that many modiiications thereof are possible. The invention, therefore, is not to be restricted except insofar as is necessitated by the plate 43 is directly proportional to the change in l Through- `prising means for compressing a test piece at-a compressive force tomain'tain constant thencrossu 2. Apparatus for ytesting plastic material ,com

- l compressionplates to compress' said ,test piece ati a predetermined rate,l acutter formaintaining' t in a plane `perpendicular to the direction for th compressive-force. and means-for indicatingfth n plates to compress said test pieceatalpredetei mined rate, means Vior maintaining constant. th n sponsive tothe pressure onssaid spring inountingl n prising'y a.v pair oicirculan compression plates ar?A ranged to receive a test pieceltherebetween, spring -1 t f mounting meansl for indicating theeilectpt prising a pair'` of plates arranged to ,applya' sub-` stantiallyverticaicompressiveforce'toa test-piece .65l Y u disposedtherebetweensprlngmountingqmeans t loix said lsupporting lmeansto' 'move said means at suchfratefrthatfsaid testLpiece' will beA coml u is movedlinearlyataScnstant,velocity.;meansf1 for moving said cam means linearly at a constant velocity, means formaintalning said testpiecein p the form` of "a cylinder having a constant cirt y t 9,280,996 prior art and 'spirit of the appended claims. .Weclaimasourinvention:` n i t j '1. `Apparatus for testing plastic material com-- predetermined rate, means for cutting o!! portions l 5 ,bulging-v from said i test; piece las a result of the"A sectional areathereof in a plane perpendicular tof mounting v.n ieans for indicating the stress-strain lationshipduringfthe test. A

for indicating ,the 'reaction yof said testl pieeetol ni0 saidstress.' vl u Qforlapplyinsa, compressive force toa' testcylinder prising a pairof compressionplates'arranged to loi'fplastie material' 'disposedftherebetweem spring receive'atest'-pieceftherebetween;spring mount y l gmountingmeausgforoneoisald platesfacamffor ing means `*for one of `said compression plates. ll5, cammeans arranged to moveythe'ther of said,

fion-maintainingtl'iediameter yo'fsaid test cylinder Y c, t www1# llllrl constant; the cross-sectionalarea ot "said t'estpiec eiect` ofthe stress on said test piece. Y

3. Apparatus for testing lasticniater'ialjco pnsing a pair ofj compressionpiatesarranged receive attest piece therebetween. spring mo t ing means for one o! said compression platesgfcam means for movingthe other otjsaidcmpression "a resting compressing u a, y'lindricai :test-pieces: `plastic cross-sectionof said test piecel including a cutter"l N y and means for rotating said cutter about the'axis forxcauslng relative:movementbetweenfsaidcut! of compression oi'ysaid testpiece, and'means-rel means for indicating for indicating" the Aei'fectvof` the compression on saidtestpiece. i u i "J5 saidtestpiece.; Y g l" 4. Apparatus for testing plastic'material Acom-l thre eect of the stress on" if t 9; Testingjpparatus'comprising a ypairoiirprising a pair of circular compression :plates` ar; -t i -cular compression-plates forreoeiving a test cylranged to receive a testfpiecetherebetween,A means l inder oi' plastic material therebetween, meansV for for moving one of said compression plates at such atrate that"v saidV test piece willbe compressedat 40'. `a constant rate, means `for `maintaining constant the cross-section of ysaid test piece Vincluding -a t cutter parallel to the axis oi!` compression of said test piece and means for -rotating said cutter about said axisgand means for indicating the 45 eirectof said stress on said test piece.-

l 5. Apparatus for testing plastic materialcomtesty cylinder` along its alcista cutting wire parallel to theaxiskof'said testcylindenmeans for rotainingl said cutting wire about said test cylinder itscross-section constant, and means for indicating the effect oi" the compression on said test cylinder. t

u lo."Testingapparatus comprising `a pair of spaced circular plates for receivingatest cylinder et plastid-material therebetween, means forcompressing said test cylinder Aalong n its `axis between said-plates, acutter for maintaining constant the mounting meansfory one `of` `said compression plates,` cam' means arranged to move the other oifsaid compression platesto compress said testAA piece at la predetermined trate' whensaid cammeans ismoved :linearlyat a constant velocity, means for moving said cam linearly atsuch con-T stant velocitypmeans for maintaining constant the `cross--section of said test-piece includl'ng""a itszaida said cutter; including a cutting, wire `disposed -parallel yto said-axis to icontact the suri y material removed by said cutting wire away from cutter and means `for rotatingsaid cutter, about `the surface-@of s aiel test 'cylderrmeans-for rothe axis oigcompression of:,saidtestfpiece;l and, tatingfsaid cutter about said axis, and means for meansresponsive*tof`the-pressurey on said Vsprinfm indicating -ithfe-leilect of t the'compression onlsaid o ssidtesc'cynjader. l

a man NADAI.

`stress on saidtest piece,

6; i Apparatus, fior. g test plastic lmaterialitci'gli'iZ-L t for the upper-ot` saidupiates, "substantially-peri pendicular supporting means carryingythel lower ofsaid platesfcammeans' engaging the lower, end

`pressed at a constant rate when saidfcam means cular crossssection including a cutting wire parallel tothe axis oi' said testpiece andjcontact- 'ingthe surface "thereonmeans for' rotating said cutting wire about said axis of said test piece, and u means responsive tothe pressure on` said spring the'direction of the compressive force,and means;V t

managing mermaid pistes at a` predates-L min edjrateggmeans i'ormoyix'igsaid camya'cutter relatively moving said` plates` to compress' saidv crossf-sectionglfsaldtest piece perpendicular to faceoif saidffiest piece and an auxiliary wire parallel said cutting wire to turn the plastic" y l, cfiiaaarsom t v i :f1-.v Testing ab 'ratus comprising a pair of plates me, anderessnmY thereof; l said e' tjeu'tting;vivire-.disposedparallell lting--eiementandjthetest piece to-maitamtne--' A diameterot saidtest piece constant, and Vmeans v f in `contact withthe surface thereof to maintain" l 

